Membrane switch technology is widely used because its production costs are relatively low as compared with the traditional full travel keyboard which contains key plunger mechanisms. Membrane switches are used additionally because of the considerable design flexibility in terms of panel layout, including the key size and shape and graphic labels. Perhaps more importantly membrane switch construction readily affords an improved enclosure, which protects the contacts thereof from hostile environments and against dust accumulation, spills and the infestation of fungi and vermin. Membrane switches afford a ready cleaning of the upper surface and a very low profile as compared with traditional key switches.
Despite these advantages, there has been some resistance to the use of membrane switches due to a perceived need for the user in feeling the movement of the switch as a tactile feedback, indicating switch closure. To answer this need, a wide variety of bubbles or dimples have been developed to be formed into the membrane or an associated layer which physically move and offer a varying force displacement characteristic favored by users. Examples of dimple membrane switches are given in U.S. Pat. Nos. 3,860,771; 3,978,297 and 4,066,851.
With the use of such dimples have come problems relating to the dimples being inverted by the pressure of closure to lock up and render the switch inoperable. This problem has manifested itself in those membrane switch constructions which are "dry", not having adhesive materials binding the various layers or laminate together. Additionally, the problem known as dimple inversion is most troublesome in switch constructions wherein there is a layer covering the dimple for sealing or other reasons. These constructions include switches having rubber or elastomer key shapes or rigid key shapes made to overlay the membrane switch site and provided with actuator projections which bear upon the dimples to effect switch operation.